System for nullifying inductive disturbances.



J. A. BARRETT.

SYSTEM FOR NULLIPYING INDUGTIVE DISTURBANGES.

'APIIQIOATION FILED APB...29. 1908.

Patented N0v. 23 1909.

til SHEBTS SHERT 1 J. A. BARRETT. v SYSTEM FOR NULLIFYING mnucnva DISTURBANGES.

APPLICATION FILED APR- 29. 1908. 940,658. Patented Nov. 23, 1909 2 SHEETS-BHEHT 2.

rn oFFicE.

JOHN A. BARRETT, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY. A CORPORATION OF NEW YORK. I

SYSTEM FOR NULLIFYING INItiIGTIVE DISTURBANCES; L

sauces.

To all whom it may concern:

Be it known that I, JOHN A. BARRETT, residing at New York, borough of Brook: lyn, in the county of Kings and State of New York, have invented certain Improvements in Systems for Nullifying Inductive Disturbances, of which the following is a specification.

Circuits for telephonic and telegraphic communication, or other lines over which electrical signals are transmitted under 'coinparatively low potentials, are liable to be subjected to inductive disturbance arising from sources external to their system, as alternating current power circuits such as are concerned in the propulsion of heavy railway trains at high speeds. These power systems frequently operate with excessive currents and at a relatively low frequency, say twenty-five cycles, and have been found to set up in adjacent conductors electromotive forces often amounting to from one hundred and fifty to three hundred volts, and sometimes attaining much higher values. Under such conditions a grounded telegraphic circuit, as usually organized, is rendered inoperative, the induced twenty-five cycle current, even if not under much pressure caus ing the relay arniatures to so vibrate that the Morse signals are rendered unintelligi' ble; lVith metallic circuits, as those of the telephone, no matter how carefully they are transposed, theystill may be seriously affected when the induced electroniotive force reaches about two hundred volts, since it then begins to discharge at the'lightning ai'resters, and to the disturbance thus produced is added the hazard of fire from insufficent insulation and of painful shocks to subscribers and operators. To prevent these difiiculties, it has been proposed to diminish the inductive effects by applying-to the disturbed conductors opposing electromotive forces generated in the plural secondary windings of one or more properly designed induction coils, there being one of these secondary windings connected 111' each s1g-.

nailing conductor, while a primary winding for inducing in the secondaries theneutralizmg electromot-iveforces is in a circuit under the same inductive influence as said signal-.

ing conductors. To attain the best results the resistance 'of the primary circuit of each Specification of Letters Patent.

induction coil must be low, and therefore the primary winding has consisted of .a conductor of relatively large cross section. To continue this low resistance-throughout the circuit of the primaries, the conductors making upthe remainder of this neutralizing circuit must also be of small resistance and since, as already pointed out, their exposure must be the same as that. of the linesinwhich disturbances are to be abated, it has been found convenient to set aside from the latter a suflicient number to give the requisiteconductivity, connecting these inmultiple to each primary winding and grounding their extremities outside the affected district to permit a flow of the primary neutralizing current. It will be evident-that the lines thus employed are useless for thepurposes for which they were intended, since their -connect-ionwith the signal primer winding makes them in effect a signal con uctor'and the ground connections carry 01f the signaling as well as the neutralizing currentsi Y There must consequently be counted against this system, in addition to the comparatively small investment in induction coils, charges for'the neutralizing conductors amounting to atleast twenty five per cent. of the expenditure for those protected. Though a gain is made, it is at a heavy-cost, and the purpose ofthe present invention is to :Hlllllinize this loss in conductors. 1 r j \Vith this end in view, my invention consists in a means of utilizing for transmission, as by telephony or telegraphy, the primary conductors, and abating therein the effect of the directly induced electroinotive forces which developin the. secondary conductors the neutralizing electroniotive forces.

In the accompanying drawings, Figure l is a diagram illustrating one embodiment of 'my invention; Fig. 2-is a front elevatiomof' a transformer adaptedfor use in. the system, andF g. 3 is a side elevation of said transforniei'. 7

Similar characters indicate like parts throughout the several figures of'the drawin s.

1eferring to Fig. 1, a grounded power Patented Novg23, 1909. Application filed April 29, 1908. Serial No. 428,370. i

conductor 1, forhigh potential, low frequenc'y alternating current, is shown extending in proximity and substantially parallel to a number of condgctors L, whichit is desired to employ for telephonic and telegraphic communication. It may be assumed that the conductors L, L, are practically equidistant-from- Z. In the present instance the; conductors are arranged in twisted pairs, and are therefore adapted for metallic telephone'cir'cuits, but they may also be used independently of their applicateen to telephone purposes or simultaneously therewith for grounded telegraph circuits, in the latter case either singly or in pairs by the wellknown composite 'orsimplex methods' The current traversing the power conductor will induce in the signalinglines electromotive forces, tending to produce the disturbing currents and discharges previously mentioned. v

In carrying out my invention I first, in the manner already outlined, divide. the lines into twogroups a and b, the conductors therein being designated L L respectively. '1 have shown three times as toms of this character, is provided with a double primary winding t foreach line in group a, so that each of the conductors L of 'a line pair is connected to one of the two conductors in a primary pair. Each transformer has a plurality of secondary Windings 6 also arranged 'inpairs, there being at least one of these for each line pair in the group 1). Thus, it will be seen that each of "the line conductors of both groups have their circuits continued through the transformers independently of the associated conductors.

For the sake of simplicity, the transformers m Fig. l of the drawings are shown without cores and with the windings separated from one another. A more correct representation of a transformer adapted for use in the present system appears in Figs. 2 and 3. A rectangular core 29, built up. of laminae of soft iron, has arranged side by side upon its opposite longer portions the desired number of primary and secondary windings or coils t and 25 these being as far .as possible symmetrically distributed, with one of the primaries alternating with a plurality of the secondaries. With one exception these coils may be'identical in construc tion, they each having preferably three hunrents used in generator ringing.

d'red and fifty turns of paired winding of number twenty lnsulated copper Wire, each conductor with a resistance. of about five be decreased by approximately ten per cent.

to secure the proper ratio of transformation. At points beyond the ends of the power conductor. Z the line conductors L are Joined to ground or some other common return at G, G, through connections which are freely permissive to currents induced through theinfluence-of the conductor Z, but which are less readily traversed by 01' are entirely impassable to signaling currents. For this purpose I have shown a conductor 10 extending to ground from each conductor L and including in series a condenser C and a retardation coil 1. The values of the capacity and inductance are preferably such that the ground connections are resonant for the particular frequency of the parasitic currents and consequently offer thereto a minimum impedance. To low frequency telegraphic impulses and to high frequency tclephonic voice currents, they present so great an impedance as to be practically exclusive, and 'e to a considerable degree so for ourv To the steady current employed in common battery telephone signaling, these ground connections are renderedentirely opaque by the presence of the condensers. They also prevent the circulation in the primaries of such earth currents as come from direct current trolley systems, and which, by magnetizing the cores of the transformers, would reduce their efliciencyf The operation of the system is as follows: The passage of thedisturbing current through the conductor Z will induce in eachof the signaling conductors L and L sulr stantially equal electromotive forces. In the primary group a, this electromotive force will cause a flow of current through the circuit furnished by the conductors L in parallel, the resonant connections and the common return, which current, traversing the primary windings t of the transformers, generates an electromotive force in eadhddf the secondary windings F. The secondary windings are so related to the primaries and so connected to the conductors L, that the transformer electromotive force of each secondary conductor opposes that directly induced by the power conducton, Then by supplying each secondary coil with a greater number of turns than its primary to provide for losses in the primary conductors and in transformation, this secondary electromotive force may be made practically to nullify the disturbing electromoms motive force. Complete compensation cannot be obtained by such a transformer, because of the. di-iierences in wave form and phase between the directly induced and sec. ondary electromotive forces in .the conductors L caused by characteristics of the transandtelegraphy between stations A and .13,

shown upon two of the lines, since the unneutralized parasitic electromotive force and the resulting current are small. The primary circuits bymy inyention are also made effective as lines of communication, since telegraph, telephone and other signaling currents are excluded from the ground connections 10, as has been previously pointed out, and may separately traverse the conductors L including the transformer primaries, used either singly as grounded circuits or in pairs as metallic circuits between stations A and B Moreover, the eii'eet upon these signaling circuits of the electromotive force which produces the primary neutralizing current is guarded against. If this were equal to the inductively impressed electromotive force it might, under some conditions of circuit and exposure, be so great as to lead to disruptive discharges, as has been described. But the transformers, by the self induction of their primaries will generate a counter electromotive force opposing-the impressed electromotive force and approaching it in magnitude, the difference being the voltage necessary to send the transformer magnetizing current through the primary circuit. formers are designed to operate efficiently and as the resistance of the primary circuit is comparatively small, thewresultant electromotive force will be too low to be detrimental. Y a The number of transformers used depends upon the length of the groups of lines to be protected and the ma ltude of the electromotive force induce since each. of said transformers will carry its proportionate part of the total voltage and to distribute this among a plurality'of Th describing the operation of the system I have referred only to the ground connections plied between any. twoof the transformers a plurality of conductors, of an induction As the transtransformers in-- creases the factor of safety in case; of acc1. indent.

and such a one has been indicated at lL- This additional ground connection constitutes a further factor of safety,-since, if one of the terminal connections should become in any way opened, partial neutralization 7 would still be secured by the transformers between remaining ground connections.

What I claim is:

1. The combination with signaling conductors arranged in groups each comprising coil having primary and secondary wincl ings included in different groups and continuing the circuit of each conductor inde-v pendently of the associated conductors.

2. A signaling system comprising groups of conductors subjected to inductive disturbance from an external source, an induc tion coil having a plurality of both primaryand secondary windings which are respectively included in different conductor groups, a common return conductor, and electrical connection between the primary conductors and return conductor, said connections tending to exclude signaling currents.

3. In a system for nullifying inductive" disturbances, the combination with electrical conductors, of an induction coil having primary and secondary windings connected to' separate groups of conductors,' means for preserving the electrical continuity of each conductor, through the induction coil independently of ,its associated conductors, a

common retu rn conductor, and'a connection to the commo return from-each ofthe con- 10'. ductors unite; to the primary windings, said connections being resonant for induced disturbing currents.

4. The combination with signaling con v ductors arranged in groups-each comprising 1-05 a plurality of conductors, of an induction coil having primary and secondary WlI1 d-' ingsincluded in different groups and continuing the circuit of each conductor inde pendently of the associated conductors and 11o ground. connections from leach of the con: ductors united to the primary winc ti ngs, sa connections being-resonant for. curr nts of a particular frequency. 3 Y

5-. An electrical system comprising two groups of conductors, a transformer having primary and secondary windings separately-c connectedin the respective groups, ground. connections from ,the primary conductors, and a condenser and retardation cluded in each ground connection.

6. An electrical signaling ystem subject .to the effects of induction and comprising two groups of; conductors, a common return conductor, a transformer having a plurality 12 of primary windings included separately in the circuits of the conductors of one group" and secondary windings united to the other group, said transformer being adapted to generate eiectromotive forces opposing those" 13$ coil in-.12(

induced in the signaling conductors, and name to this specification in the presence of connections between the conductors of the two subscribing Witnesses, this 24th day of primary group and the common return con- April 1908. ductor, said connections ofiering a 10w im- JOHN A. BARRETT. 5 pedance to the induced currents and a rela- Witnesses:

' tively high impedance to signaling currents. ROBERT FOSTER J ANEs,

SYLvANUs H. COBB.

In testimony whereof, I have signed my 

